Characterization of Stratospheric Clear Air Turbulence for Air Force Platforms

Abstract

Stratospheric mechanical turbulence (altitudes 12-25km) is characterized by patchy high frequency fluctuations in the stratospheric wind fields and long-lived energetic eddies with a few hundred meters scales in the vertical. The thin clear air turbulence (CAT) layers negatively impact the effective control, stability and performance of the newest generation of unmanned air vehicles (UAV) such as the Global Hawk. Flying through stratospheric CAT causes the autopilot to begin pitch oscillations that seriously degrade photographic and synthetic aperture radar performance as well as putting the platform itself at risk. While there is a need for a real-time forecast of these thin stratospheric CAT layers, these cannot be resolved by even the latest generation of weather research and forecasting (WRF) mesoscale meteorological codes. Some of the objectives of this challenge project are to influence the development of the next generation mesoscale numerical weather prediction codes for the lower stratosphere, by improving subgrid-scale parametrization of nonhomogeneous, anisotropic, non-Kolmogorov, patchy shear stratified stratospheric turbulence; and to enable forecasting of nonlinear, non-monochromatic inertia-gravity waves with large horizontal wavelengths (few hundred kilometers) which generate thin (few hundred meters) CAT layers